服部 克巳

Abstract Numerous studies have reported anomalous ultralow frequency (ULF) electromagnetic fields preceding earthquakes. In this paper, we estimate the current intensity responsible for generating the earthquake‐related ULF fields under the assumption that the origin is a current flowing at the hypocenter and that it has the same frequency dependence for all cases. To estimate current intensity, we perform ULF electromagnetic field simulations with an absorbing boundary condition developed in this study, taking into account the conductivity distribution of the Earth's crust. We analyze 11 earthquakes, including those that occurred in Loma Prieta, Spitak, Guam, Biak, Kagoshima, Iwateken Nairiku Hokubu, Izu swarm, Jammu and Kashmir, Alum Rock, Wenchuan, and L’Aquila. Our results show that, for nine out of the 11 events, there is a positive correlation between current intensity and earthquake magnitude, suggesting that the measured ULF fields originate from seismic activity and supporting our assumptions.

<jats:title>Abstract</jats:title><jats:p>The China Seismo-Electromagnetic Satellite (CSES), with a sun-synchronous orbit at 507 km altitude, was launched on 2 February 2018 to investigate pre-earthquake ionospheric anomalies (PEIAs) and ionospheric space weather. The CSES probes manifest longitudinal features of four-peak plasma density and three plasma depletions in the equatorial/low-latitudes as well as mid-latitude troughs. CSES plasma and the total electron content (TEC) of the global ionosphere map (GIM) are used to study PEIAs associated with a destructive M7.0 earthquake and its followed M6.5 and M6.3/M6.9 earthquakes in Lombok, Indonesia, on 5, 17, and 19 August 2018, respectively, as well as to examine ionospheric disturbances induced by an intense storm with the Dst index of − 175 nT on 26 August 2018. Anomalous increases (decreases) in the GIM TEC and CSES plasma density (temperature) frequently appear specifically over the epicenter days 1–5 before the M7.0 earthquake and followed earthquakes, when the geomagnetic conditions of these PEIA periods are relatively quiet, Dst: − 37 to 19 nT. In contrast, TEC and CSES plasma parameter anomalies occur globally in the southern hemisphere during the storm days of 26–28 August 2018. The CSES ion velocity shows that the electric fields of PEIAs associated with the M7.0 earthquake are 0.21/0.06 mV/m eastward and 0.11/0.10 mV/m downward at post-midnight/post-noon on 1–3 August 2018, while the penetration electric fields during the storm periods of 26–28 August 2018 are 0.17/0.45 mV/m westward/downward at post-midnight of 02:00 LT and 0.26/0.26 mV/m eastward/upward at post-noon of 14:00 LT. Spatial analyses on CSES plasma discriminate PEIAs from global effects and locate the epicenter of possible forthcoming large earthquakes. CSES ion velocities are useful to derive PEIA- and storm-related electric fields in the ionosphere.</jats:p>

The Gutenberg-Richter b value describes the ratio between large and small events. A number of studies have suggested that the b value decreases before large earthquakes. In this study, we investigate the temporal variation of the b value of an area along the main rupture zone of the 2008 Wenchuan earthquake (M8.0) prior to the great event. Before estimating b values, we tested the earthquake catalog to make sure that we use the reliable frequency-magnitude distribution by the calculation of MC (completeness of magnitude). We define parameter P (Delta AIC >= 2) values to examine the significance level of b-value changes in the temporal variation by combining a boostrap method with Akaike's Information Criterion (AIC). The b value in the main rupture zone shows a long-term decrease trend. We then focus on a smaller area where the initial rupture starts. The results show that b values significantly changed about 3 months before the 2008 Wenchuan earthquake in the initial rupture area, indicating that the b value has a potential capability to monitor and detect precursory phenomena of great earthquakes.

Early studies have shown evidence of the seismo-ionospheric perturbations prior to large earthquakes. Due to dynamic complexity in the ionosphere, the identification of precursory ionospheric changes is quite challenging. In this study, we analyze the total electron content (TEC) in the global ionosphere map and investigate the TEC changes prior to M ≥ 6.0 earthquakes in the Chinese Mainland during 1998–2013 to identify possible seismo-ionospheric precursors. Singular spectrum analysis is applied to extract the trend and periodic variations including diurnal and semi-diurnal components, which are dominated by solar activities. The residual ΔTEC which is mainly composed of errors and possible perturbations induced by earthquakes and geomagnetic activities is further investigated, and the root-mean-square error is employed to detect anomalous changes. The F_10.7 and Dst index is also used as criterion to rule out the anomalies when intense solar or geomagnetic activities occur. Our results are consistent with those of previous studies. It is confirmed that the negative anomalies are dominant 1–5 days before the earthquakes at the fixed point (35°N, 90°E) during 0600–1000 LT. The anomalies are more obvious near the epicenter area. The singular spectrum analysis method help to establish a more reliable variation background of TEC and thus may improve the identification of precursory ionospheric changes.

In order to monitor temporal and spatial crustal activities associated with earthquakes, ground- and satellite-based monitoring systems have been installed in China since the 1990s. In recent years, the correlation between monitoring strain anomalies and local major earthquakes has been verified. In this study, we further evaluate the possibility of strain anomalies containing earthquake precursors by using Receiver Operating Characteristic (ROC) prediction. First, strain network anomalies were extracted in the borehole strain data recorded in Western China during 2010–2017. Then, we proposed a new prediction strategy characterized by the number of network anomalies in an anomaly window, Nano, and the length of alarm window, Talm. We assumed that clusters of network anomalies indicate a probability increase of an impending earthquake, and consequently, the alarm window would be the duration during which a possible earthquake would occur. The Area Under the ROC Curve (AUC) between true predicted rate, tpr, and false alarm rate, fpr, is measured to evaluate the efficiency of the prediction strategies. We found that the optimal strategy of short-term forecasts was established by setting the number of anomalies greater than 7 within 14 days and the alarm window at one day. The results further show the prediction strategy performs significantly better when there are frequent enhanced network anomalies prior to the larger earthquakes surrounding the strain network region. The ROC detection indicates that strain data possibly contain the precursory information associated with major earthquakes and highlights the potential for short-term earthquake forecasting.

In order to find out whether the geomagnetic storms and large-mega earthquakes are correlated or not, statistical studies based on Superposed Epoch Analysis (SEA), significance analysis, and Z test have been applied to the Dst index data and M ≥ 7.0 global earthquakes during 1957–2020. The results indicate that before M ≥ 7.0 global earthquakes, there are clearly higher probabilities of geomagnetic storms than after them. Geomagnetic storms are more likely to be related with shallow earthquakes rather than deep ones. Further statistical investigations of the results based on cumulative storm hours show consistency with those based on storm days, suggesting that the high probability of geomagnetic storms prior to large-mega earthquakes is significant and robust. Some possible mechanisms such as a reverse piezoelectric effect and/or electroosmotic flow are discussed to explain the statistical correlation. The result might open new perspectives in the complex process of earthquakes and the Lithosphere-Atmosphere-Ionosphere (LAI) coupling.

© 2020 Elsevier Ltd In this study, we investigated the characteristics of pre-earthquake ionospheric effects related to four successive shallow-focus earthquakes (M6.4 on July 28, 2018, M6.8, 5.9, 6.9 on August 05, 09 and 19, 2018) in Indonesia by the China Seismo-Electromagnetic Satellite (CSES). By adopting the moving median method (MMM), the ionospheric electron density (Ne) detected by the Langmuir probe (LAP) onboard CSES presented remarkable enhancements along the orbits #2660-0 on July 27, #2721-0 and #2728-1 on July 31, #2827-0 and #2735-1 on August 7, #2934-0 on August 14, respectively, which were just 1, 5, 2 and 5 days before the four earthquakes. Moreover, the disturbances mainly appeared in the north and north-east within the distance of 2000 km from each epicenter. By comparing the disturbed orbits with their corresponding four nearest and four revisiting orbits as well as the predicted values from the International Reference Ionosphere 2016 model (IRI-2016), the results powerfully illustrated that CSES observed the ionospheric precursors preceding the four Indonesian earthquakes. To make the space-borne results more convincing, we further studied the grid total electron content (TEC) data from the Center for Orbit Determination in Europe (CODE), which exhibited similar anomalies in both the temporal and spatial distributions. In the end, the superposed epoch analyses (SEA) method was conducted on 35 M ⩾ 5.8, depth⩽50 km earthquakes in Indonesia during 2007–2017 by using CODE TEC. The statistical results demonstrated that there were significant positive anomalies 1–7 days before earthquakes within 2000 km from the epicenters in this region. The positive plasma perturbations detected by CSES were highly suggested as the seismic-ionospheric effects before earthquakes.

© 2020 by the authors. In order to clarify ultra-low-frequency (ULF) seismomagnetic phenomena, a sensitive geomagnetic network was installed in Kanto, Japan since 2000. In previous studies, we have verified the correlation between ULF magnetic anomalies and local sizeable earthquakes. In this study, we use Molchan's error diagram to evaluate the potential earthquake precursory information in the magnetic data recorded in Kanto, Japan during 2000-2010. We introduce the probability gain (PG') and the probability difference (D') to quantify the forecasting performance and to explore the optimal prediction parameters for a given ULF magnetic station. The results show that the earthquake predictions based on magnetic anomalies are significantly better than random guesses, indicating the magnetic data contain potential useful precursory information. Further investigations suggest that the prediction performance depends on the choices of the distance (R) and size of the target earthquake events (Es). Optimal R and Es are about (100 km, 108.75) and (180 km, 108.75) for Seikoshi (SKS) station in Izu and Kiyosumi (KYS) station in Boso, respectively.

© 2020 by the authors. We proposed a cloud discrimination method applicable in Japan using MODIS nighttime data, monitored the singularity of the spatiotemporal correlation of surface temperature anomalies and investigated the possibility of detecting and monitoring lava activity in Shinmoedake. With the aim to detect lava eruption activity in 2011, nine years of data from 2003 to 2011 were analyzed. As a result, the first anomalous singularity in brightness temperature was detected on 26 January 2011. Moreover, the maximum value was detected on 30 January 2011. The values showed larger ones until early February 2011. When an anomalous singularity appeared, it was the only period with the magma-related volcanic activity for Shinmoedake over the analyzed period of nine years. The above facts indicate the effectiveness of the proposed singularity method to monitor the lava activity for Shinmoedake. Therefore, it is concluded that if cloud discrimination is realized with high accuracy, no spurious changes will come to arise, and no false detection of hotspots will be given.

© 2019, Springer Nature Switzerland AG. We investigated observational data from 20 geomagnetic observatories at longitudes of 130°E to 150°E between 2009 and 2012 in order to detect possible anomalous changes in the geomagnetic solar quiet daily (Sq) variation related to the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0) that occurred on March 11, 2011, in Japan. We selected the five quietest days in every month and analyzed three-component magnetic data with 1-min resolution using the natural orthogonal component method to identify Sq variations from observations, and performed spherical harmonic analysis (SHA) to separate the internal and the external equivalent Sq current systems of Je and Ji. We found that Je and Ji were distorted near the epicenter on two geomagnetic quiet days, January 23 and 27, 2011. This was about 2 months before the earthquake. We then employed backward computation on the external and internal parts of the SHA model geomagnetic fields, Be and Bi, to determine the possible anomalous magnetic field variations at each station. The results showed significant differences in daily variation for all components on January 23 and 27, 2011. On the other days, we could not recognize any apparent anomalous behaviors apart from known secular, seasonal, and solar activity dependence. A possible connection between this anomaly and the very strong Tohoku earthquake, which followed only 1.5 months after the geomagnetic anomaly, is of extreme interest for research on earthquake precursors.

© 2019 World Scientific Publishing Company. Tsunami waves can induce tsunami traveling ionospheric disturbances (TTIDs) of the total electron content (TEC). In this study, we examine the TEC derived by ground-based receivers of the global positioning system (GPS) and identify TTIDs induced by 2004 Indian Ocean tsunami. Simulations of the COMCOT (Cornell multi-grid coupled tsunami) model and analyses of the circle method, the ray-tracing technique, and the beam-forming technique are used to show that TTIDs can be quickly detected and confirmed after the tsunami occurrence. Finally, the ionospheric TEC derived by existing ground-based GNSS (Global Navigation Satellite Systems) receiving stations is demonstrated to be useful to support the tsunami early warning system.

© 2019 Published under licence by IOP Publishing Ltd. Ultrasonic wave is suitable to be used as information carrier in short-range remote sensing practices. When developing a short-range ultrasonic remote sensing device, the object distance measurement routine shall produce an accurate result. In a few-meter or several-meter object detection or imaging, millimeter accuracy is required, therefore, a calibration becomes crucial. This article addresses the process and the result of our research on calibrating the distance between the device and the backscattering object. Our approach consists of investigating potential delay contributors, recognizing the practical delay contributors by analysing the program routine, formulating the calibration equation and applying the calibration equation in the computation.

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. In this work, we assessed the possible relation of ionospheric perturbations observed by Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER), Global Positioning System total electron content (GPS TEC), National Oceanic and Atmospheric Administration (NOAA)-derived outgoing longwave-Earth radiation (OLR), and atmospheric chemical potential (ACP) measurements, with volcanic and Saharan dust events identified by ground and satellite-based medium infrared/thermal infrared (MIR/TIR) observations. The results indicated that the Mt. Etna (Italy) volcanic activity of 2006 was probably responsible for the ionospheric perturbations revealed by DEMETER on 4 November and 6 December and by GPS TEC observations on 4 November and 12 December. This activity also affected the OLR (on 26 October; 6 and 23 November; and 2, 6, and 14 December) and ACP (on 31 October-1 November) analyses. Similarly, two massive Saharan dust episodes, detected by Robust Satellite Techniques (RST) using Spinning Enhanced Visible and Infrared Imager (SEVIRI) optical data, probably caused the ionospheric anomalies recorded, based on DEMETER and GPS TEC observations, over the Mediterranean basin in May 2008. The study confirmed the perturbing effects of volcanic and dust events on tropospheric and ionospheric parameters. Further, it demonstrated the advantages of using independent satellite observations to investigate atmospheric phenomena, which may not always be well documented. The impact of this increased detection capacity in reducing false positives, in the framework of a short-term seismic hazard forecast based on the study of ionospheric and tropospheric anomalies, is also addressed.

© 2019 by the authors. The Gutenberg-Richter Law describes the frequency-magnitude distribution of earthquakes. A number of studies have shown that the slope (b value) of the relationship between frequency and magnitude decreased before large earthquakes. In this paper, we investigate the temporal variation of the b value off the Pacific coast of Tokachi, Hokkaido, Japan, during 1990-2014. The magnitude of completeness (Mc) in the catalog is evaluated by combining the maximum curvature (MAXC) technique and the bootstrap approach. Then, the b value, and its uncertainty, is computed by using the maximum likelihood estimation. The Akaike Information Criterion (AIC) with the bootstrap approach is introduced to statistically assess the temporal variation of b values and quantify the significance level. The results show a decrease in trends of the b value prior to two large earthquakes (26 September 2003 (M8.0) and 11 September 2008 (M7.1)) in the analyzed area. In addition, the decrease of b values shows certain statistical significance three months before the 2003 Earthquake off the Pacific coast of Tokachi (M8.0). It is concluded that the b value with statistical assessment may contain potential information for future large earthquake preparation off the Pacific coast of Tokachi, Hokkaido, Japan.

© 2019, Science Press. All right reserved. Along with the development of urban constructions, artificial disturbances in geomagnetic observations are becoming more and more tremendous. The near-field noises produced by human activities such as vehicles, subway and high-speed railways make it difficult to precisely measure geomagnetic pulsations on the ground, thus reducing the practical application value of geomagnetic data. Therefore, suppressing near-field noises has scientific significance and application value. In this study, by combining remote reference and blind source separation analysis methods, we proposed a new signal processing approach which is able to separate geomagnetic pulsation from near-field noise. First, we demonstrated the effectiveness of the new approach by separating signals of different sources in the simulation analysis. Then, we applied this method to geomagnetic field data observed in Chiba, Japan where DC-driven train noises were intense. The results showed that geomagnetic pulsations and train noises are separated clearly, and near-field train noise could be reduced effectively on that basis. It is concluded that the reference-based blind source separation analysis is useful in extracting geomagnetic pulsations and suppressing near-field noises, and may have potential application value in electromagnetic exploration.

© 2019, Electromagnetics Academy. All rights reserved. In this paper, a circularly polarized slot-patch antenna for nanosatellite is presented. The novel design of the circularly polarized wave conducted by two asymmetrical rectangular-truncation techniques implemented on a circularly-slotted-patch on the front side and a deformed-shifted-feedline on the back side of the substrate. The antenna is printed on substrates with the dielectric constant of 2.17 and thickness of 1.6mm. The resonant frequency of the proposed antenna is set at 2.2 GHz with the minimum requirement of the axial ratio bandwidth (ARBW) of 300 MHz. The proposed antenna produces under 10 dB impedance bandwidth (IBW) 1.2765 GHz or equal to 58% (1.7235-3 GHz) with Left-Handed Circular Polarization (LHCP). The average antenna gain reaches 4.5 dBic at 2.2 GHz and the ARBW 327.5MHz or about 14.88% (2.0275-2.355 GHz). This paper includes the description and presentation of the completed discussion.

© 2018, Science Press. All right reserved. The Gutenberg-Richter Law describes the frequency-magnitude distribution of earthquakes. A number of studies have shown that the slope (b value) of the relationship between frequency and magnitude decreased before large earthquakes. Based on the analysis of the earthquake catalog from January, 2000 to April, 2008, we have investigated seismicity change and b value variation prior to the MS8.0 Wenchuan earthquake. The results show clear drops of both monthly and quarterly frequency of earthquakes during 2005-2006. The b value exhibits a long-term decrease trend since 2002, and reaches to the minimum just before the onset of the main shock. The temporal variation of b value is quite similar to that prior to the MW9.0 Tohoku earthquake in Japan, which may reflect the stress evolution during the preparation process of large earthquakes. These results indicate that the b value is an important indicator of an impending great earthquake, and has high potential in terms of predicting a future large quake.

© 2017 Wiley Periodicals, Inc. In order to mitigate landslide risks, monitoring of ground water is essential. Previous indoor experiments suggest that the self-potential approach has an advantage to establish the early warning system in performance to detect related signals and in cost. To evaluate results obtained from the previous indoor experiments, in situ measurements are required. To achieve this, we selected a test slope at Nishiikawa, Tokushima, Japan and we performed preliminary electrical resistivity exploration (ERT) and core-sampling. The results of ERT show that there are low resistive areas in shallow depth (<3 m). The core-sampling results also indicate that there exists the structure which corresponds to slip surface. In addition, anisotropy in magnetic susceptibility was examined and the samples around the estimated slip surface region provide the oblate ellipsoid characteristics. These results of ERT and core analyses are consistent and make convince the identification of the slip surface. Based on these preliminary results, we set up the in situ self-potential observation at the slope and started measurements.

This paper utilizes 10 stations of co-located seismometer, QuakeFinder/infrasound to observe co-seismic signatures triggered by the 6 February 2016 M6.6 Meinong Earthquake. Each QuakeFinder system consists of a 3-axes induction magnetometer, an air conductivity sensor, a geophone, and temperature/relative humidity sensors. There are no obvious charges in the positive/negative ions, the temperature, and the humidity, while the magnetometer, the geophone, and infrasound data detect clear co-seismic signatures, similar to seismic waves recorded by seismometers. The magnetometers register high-frequency pulsations, like seismic waves, and superimpose with low-frequency variations, which could be caused by the magnetometer shaking/tilting and/or the underground water level change, respectively, upon the arrival of seismic waves. The spectrum centering around 2.0 Hz of the co-seismic geophone fluctuations is similar to that of the seismic waves. However, the energy of co-seismic geophone fluctuations (also magnetometer pulsations) yields an exponential decay to the distance of a station to the epicenter, while the energy of the seismic waves is inversely proportional to the square of the distance. This suggests that the mechanisms for detecting seismic waves of the QuakeFinder system and seismometers are different. In general, the geophone and magnetometer/infrasound system are useful to record high- and low-frequency seismic waves, respectively.

© 2017 Wiley Periodicals, Inc. Study of the electric self-potential (SP) and the magnetic field was conducted at the explosion seismic experiment in Ooyama, Toyama Prefecture. The explosion was induced by 450-kg gun powder placed at a depth of 32.2 m to 75 m. The SP was measured by four electrodes arranged in a line crossing the explosion point, where the distance of each electrode from the explosion ranged from 10 m to 100 m. Induced SP changes consisted of two portions, namely, fluctuations with shorter period (∼10 ms) and fluctuations with longer periods (∼50 ms). Regarding the latter, the amplitude was in proportion to the span length of electrode couples and the fluctuations arrived faster at the electrode couples nearer to the explosion. Furthermore, the increment of ground level in SP was observed in each electrode couple after the explosion, which was concordant with the distribution of apparent resistivity underground studied by the survey. The magnetic field measured by the fluxgate magnetometer at the site 35 m north from the explosion also showed change of a few nT after the explosion. This may have been caused by change of magnetic properties underground.

© The Authors 2016. Previous statistical studies showed that there was a correlation between the ultralow frequency (ULF) seismo-magnetic phenomena and local seismicity in the Kakioka region, Japan. In this study, utilizing Molchan's error diagram, we evaluate whether these phenomena contain precursory information and discuss how they can be used in short-term forecasting of sizable earthquakes. In practice, for given series of precursory signals and related earthquake events, each prediction strategy is characterized by the leading time of alarms (Δ) and the length of alarm window (L). The leading time is the time length between a detected anomaly and its following alarm, and the alarm window is the duration that an alarm lasts. A modified area skill score measuring the area between actual prediction curve and random prediction line in Molchan's error diagram is used to assess the efficiency of different prediction strategies. The results indicate that predictions based on ULF magnetic data in Kakioka, Japan perform better than random prediction when Δ is around 1 week and L is less than 4 d or Δ is 13-14 d and L is less than 1 week. The optimal strategy of short-term forecasts has been established by setting Δ at 8 d and L at 1 d. The methodology proposed in this study could also be useful in evaluating the prediction policy and optimizing other kinds of measurements for short-term earthquake forecasting.

? 2017 The Institute of Electrical Engineers of Japan. Recent studies have reported unusual behaviors of geomagnetic diurnal variation (GDV) in the vertical component prior to the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0). To make a better understanding of this phenomenon, time-spatial analysis of GDV has been applied in this study. Geomagnetic data of long term observations at 17 stations in Japan have been analyzed using the same method in Han et al. 2015. Ratios of diurnal variation range between the target station and the reference station KAK have been computed. After removing seasonal variations revealed by wavelet transform analysis, the 15-day mean values of the ratios in the vertical component shows a clear anomaly exceeding the statistical threshold about 2 months before the mega event in both ESA and MIZ stations in the Tohoku Region. Similar results could not be found in other regions of Japan. Spatial distributions of the ratios show a good agreement between the location of the anomalies and the epicenter of Mw 9.0 earthquake. These time-spatial results are consistent with independent results obtained from other observations such as radon density, seismicity, and GPS displacements, which suggest the geomagnetic data might be useful in earthquake monitoring and disaster mitigation.

© 2016 Xu et al. (2013) and Han et al. (2015) have reported unusual behaviors of geomagnetic diurnal variation (GDV) in the vertical component prior to the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0). To make a better understanding of this phenomenon, temporal-spatial analyses of GDV have been applied in this study. Geomagnetic data of long-term observations at 17 stations in Japan have been analyzed using the same method in Han et al. (2015). Ratios of diurnal variation range between the reference station KAK and the target stations have been computed. After removing seasonal variations, the 15-day backward running mean values of the ratios in the vertical component shows a clear anomaly exceeding the statistical threshold about 2 months before the mega event at both ESA and MIZ stations in the Tohoku Region. Locations of anomalies in spatial distribution show a good correlation with the epicenter of the Mw 9.0 earthquake. These spatiotemporal results are consistent with those obtained from other independent observations such as groundwater level and GPS displacements. The coupling of multiple pre-earthquake phenomena may help to understand the preparation process of a mega earthquake in the subduction zone.

© 2016 Wiley Periodicals, Inc. A numerical simulation has been performed to evaluate the performance of ionospheric tomography using the residual minimization training neural network (RMTNN) method. The results indicate that reconstruction with high precision is possible when the standard deviation of the noise is about 2.5% or less of the average value of the observed data (slant total electron content [STEC]). Moreover, in the daytime, when the value of STEC becomes large, the signal to noise ratio (SNR) increases and the reconstruction accuracy becomes high; at night when the SNR falls, conversely, it becomes low. The results of detectability tests show that the RMTNN method has a good performance at about F-layer height with shape and peak intensity reconstruction. In conclusion, the newly developed RMTNN ionospheric tomography is effective in reconstructing the 3D electron density distribution from realistic STEC data in the daytime, and is able to estimate images around the F-layer.